<template>
  <div>
    我是son元素 {{ title }}
    <button @click="changeFn">修改title</button>
  </div>
</template>

<script>
export default {
  props: ["title"],
  methods: {
    changeFn() {
      this.$emit("changeTitle", "那为什么刚才就只能触发一次呢？");
    }
  }
};
</script>

<style scoped>
div {
  border: 3px solid #000;
  padding: 10px;
}
</style>